1 Field of the Invention
The present invention relates to a gas barrier sheet, and more particularly, to a gas barrier sheet that has good transparency and high heat resistance, hardly curls, and is excellent in the adhesion between its constituent films, in hard coating property and in gas-barrier properties.
2. Background Art
Attempts to attain a high level of gas-barrier properties by forming, on substrate films, thin films of inorganic or organic materials have been made so far.
In Japanese Laid-Open Patent Publication No. JP2005-313560 is presented a gas barrier film having a layered structure composed of a flexible substrate, an acrylic resin layer with a thickness of 0.1 to 10 μm, that is a hardened layer of a UV-curing resin containing, as a polymerizable component, an acrylic monomer and/or a polymerizable acrylic prepolymer alone, and an inorganic barrier layer with a thickness of 20 to 100 nm, the acrylic resin layer and the inorganic barrier layer being situated on one side or both sides of the substrate in the order named.
According to the above publication, if a hardened layer of the above specified UV-curing resin, having a specified thickness, is formed directly on a flexible substrate, and an inorganic barrier layer with a specified thickness is further formed on the hardened resin layer, a gas barrier film having excellent gas-barrier properties can be obtained without experiencing curling in its production process. And SiOx, AlOx, SiOxNy, SiNx, SiOxNyCz, SiNxCy, AlOxNy, AlNx, AlOxNyCz, AlNxCy, etc. are enumerated as examples of ceramic materials useful for the inorganic barrier layer.
Japanese Laid-Open Patent Publication No. IP8-295848 (1996) describes a surface-treated resin-made material that is a resin-made material whose one or both surfaces are treated with a specified composition for surface treatment. The composition for surface treatment comprises an organic compound (A) for making the composition film to be formed flexible, a compound (B) having in its molecule a functional group that can react with amino group in the organic compound (A), a specified organometallic compound (C), and a solvent (D). Specifically, in Example 1 described in this patent publication, polyethyleneimine is used as the organic compound (A), γ-glycidoxy-propyltrimethoxysilane as the compound (B), tetramethoxysilane as the compound (C), and methanol as the solvent (D).
In Japanese Laid-Open Patent Publication No. JP2005-313560, by combining an acrylic resin film with a specified thickness and a gas barrier film made from an inorganic material, having a specified thickness, a gas barrier sheet having both gas-barrier properties and anti-curl properties is produced.
In the above Japanese Laid-Open Patent Publication No. JP2005-313560, however, the acrylic resin film tends to yellow with heat when the gas barrier sheet is thermally treated, in the post-production process, under more severe conditions for the purpose of producing a multi-layer structure or for annealing. Yellowing of the acrylic resin film makes the gas-barrier sheet yellowish. Thus the gas-barrier sheet described in this publication still remains unsatisfactory in heat resistance.
Also the surface-treated resin-made material (hereinafter referred to as a “gas barrier sheet”) that is a resin-made material whose one or both surfaces are treated with a specified composition for surface treatment, described in the above Japanese Laid-Open Patent Publication No. JP8-295848, was found to be still unsatisfactory in gas-barrier properties, transparency, heat resistance and anti-curl properties.
Namely, when the intended use of a gas barrier sheet is a liquid crystal display, an organic EL display, or the like, the gas barrier sheet is usually required to have such excellent gas-barrier properties that its water vapor permeability is 0.1 g/m2/day (g/m2·day) or less, and that its oxygen permeability is 0.1 cc/m2/day·atm (cc/m2·day·atm) or less. However, the gas barrier sheet described in the above Japanese Laid-Open Patent Publication No. JP8-295848 cannot exhibit such excellent gas-barrier properties, as shown in Examples described in the publication.
Further, when the intended use of a gas barrier sheet is an organic EL display or the like, it is desirable that the gas barrier sheet be highly transparent. However, in Japanese Laid-Open Patent Publication No. JP8-295848, since the organic compound (A) is used for making the film to be formed flexible, the film formed contains an increased number of organic functional groups and thus tends to have light absorption in the visible light range. Consequently, the gas barrier sheet described in this publication tends to have decreased transparency. Thus transparency also remains a problem with this gas barrier sheet.
Furthermore, due to the organic compound (A), a large number of organic functional groups are present in the film formed, so that the gas barrier sheet is readily colored when thermally loaded. Thus heat resistance is another problem with the above gas barrier sheet.
Moreover, when the intended use of a gas barrier sheet is an organic EL display or the like, it is desirable that the gas barrier sheet hardly curl even when held at high temperatures, if the production process of an organic EL display or the like is taken into account. However, in Japanese Laid-Open Patent Publication No. JP8-295848, the organic compound (A) is used to make the film to be formed flexible, so that the film formed contains an increased number of organic functional groups and thus has increased film stress. Consequently, the gas barrier sheet described in this publication easily curls. Thus this gas barrier sheet is unsatisfactory also from the viewpoint of curling prevention.
The present invention was accomplished in order to solve the above-described problems in the prior art. An object of the present invention, therefore, is to provide a gas barrier sheet excellent in transparency, heat resistance, anti-curl properties, and gas-barrier properties. Another object of the invention is to provide a gas barrier sheet having the following advantages in addition to the above properties: the sheet is excellent in hard coating property (i.e., can satisfactorily serve as a hard coating) and also in the adhesion between its constituent films. Particularly, an object of the invention is to provide a gas barrier sheet that remains uncurled and retains its gas-barrier properties even after it has undergone a heat cycle test which is carried out to test the durability of an organic EL display or the like.